The present invention relates to apparatus for straining liquids.
According to the present invention an apparatus for straining liquids comprises a straining screen, means mounting the screen for vibration, means operable to vibrate the screen, means for containing a body of liquid to be strained on top of and in contact with the screen, means for supplying liquid to be strained to the containing means and having a valve operable to halt the supply, a level detector in the containing means and control means automatically responsive to detection by the level detector of a liquid level in the containing means above a predetermined maximum level to operate the valve to halt the liquid supply to the containing means. In operation the vibration of the screen of the above straining apparatus considerably increases the time during which liquid can be strained before the screen becomes blocked or blinded by accumulated solids strained out of the liquid. Thus, the "down time" of the apparatus can be reduced. Furthermore, the automatic control means ensures that the supply of liquid to be strained is halted to prevent overflow of the containing means. In this way the apparatus can be left to operate without the need for an operator continuously monitoring the liquid level above the straining screen to guard against spillage.
Very conveniently, the container means is arranged to enclose substantially completely the body of liquid to be strained. Such an arrangement is rendered practicable by the provision of the automatic control means, since otherwise the container means must be open so that an operator can view the liquid level. By making the container means substantially completely enclosed any noxious gases or solvents given off by the liquid to be strained are prevented from reaching the atmosphere. This has special advantages when the apparatus is used for straining paints, since, not only is the contamination of the atmosphere by solvent vapours from the paint reduced, but the evaporation of the solvents from the paint is itself reduced, thus reducing the tendency of the paint to set or skin during straining.
In one embodiment, the containing means comprises an upwardly extending skirt sealed around the periphery of the screen and a cover extending inwardly from the top of the skirt over the screen, a flexible connection being provided between the container means and the liquid supply means.
Preferably the straining apparatus includes a buffer tank disposed below the screen and arranged to receive the liquid passing through the screen. The buffer tank enables strained liquid to be stored for delivery for further processing as required. Very conveniently, the buffer tank is disposed immediately beneath the screen, so that the liquid passing through the screen can fall directly into the tank. Then means may be provided for directing liquid passing through the screen into the buffer tank, and a flexible coupling may be provided between the tank and such directing means, so that liquid in the buffer tank is substantially completely enclosed.
It will be appreciated that the flexible coupling between the buffer tank and the directing means and the flexible connection between the containing means and the liquid supply means allow for the vibration of the straining screen during operation of the apparatus.
Preferably a second level detector is provided in the buffer tank for detecting a maximum level in the tank, and the control means is automatically responsive also to the detection by the second detector of the maximum level to operate the valve to halt liquid supply to the container means. In this way the supply of liquid to be strained is cut off when the buffer tank becomes nearly full. It will be appreciated that the maximum level in the buffer tank detected by the level detector is selected to enable any remaining body of unstrained liquid above the strainer in the containing means to pass through the strainer without causing the buffer tank to overflow.
In one embodiment, the means operable to vibrate the screen includes two out of balance weight assemblies on opposite sides of the screen and rotatable substantially in the same plane as the screen, and a motor connected to rotate the assemblies so that the screen vibrates substantially in its own plane.